Adjustable toroidal inductance



March 1, 1955 H. B. REX

ADJUSTABLE TOROIDAL INDUCTANCE Filed June 30, 1952 INVENTbk B. REX

HAROL D ATTORNEYS United States Patent 2,703 92 ADJUSTABLE TOROIDAL INDUCTANOE Harold B. Rex, Falls Church, Va. Appl cation. June 30, 1 2 .ssr aiblo- 2 6 52 6 Cla ms. (Cl. 331 :1130) (Granted under Title 35, U. S. C0de'(1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon orthere for.

The present invention relates to a nominally fixed inductance having means for making a correcting adjustment and more particularly to an inductance having a toroidal core made from a spiral strip of ferromagnetic material, the spacing between at least some of the convolutions of the spiral being adjustable to vary the working or effective permeability. of the core.

The principal advantage 'of toroidal cores when used in transformers, filters, bridges etc.; namely, the reduction of the amount of stray magnetic flux to a minimum, has long been known. However, such coils have had a rather limited use where a precise value of the inductance is required. The value of the inductance of a given coil can be determined if the number of turns of the conductor in the coil, the cross sectional area of the core, the mean radius of the core, and the permeability of the core are known. The permeability of the core varies as a result of its hysteresis as well as of its composition. Because it is impossible to control the permeability of the core with sufficient accuracy, it has been impossible to mass produce toroidal inductances which have a predetermined value.

The prior art has solved this problem in two different ways. One way is to connect a variable inductance in series with a toroidal inductance. When they are connected in series, the values of the inductances add so that it is possible to make adjustments of the value of the inductance of the two coils. This of course has the disadvantage of requiring two inductances instead of one. Other toroidal inductances locate pieces of ferromagnetic material in the vicinity of the toroid, and by the size,

shape and location of the pieces, it is possible to vary.

the effective or working value of the permeability of the core. This method has the disadvantages of causing considerable leakage of magnetic induction, and also increases the size of the inductances so that they are not suitable for applications in which the available space is limited.

The present invention relates to a new and improved means for adjusting the permeability of a toroidal inductance after the inductance has been assembled, and which overcomes the deficiencies of prior toroidal inductances. In an inductance according to this invention there is provided a hollow toroidal housing or casing of substantially nonmagnetic material about which is wound a coil of an insulated conductor. Located within the housing is a core of ferromagnetic material which can be made by winding a thin ribbon of a suitable ferromagnetic material into a spiral. The convolutions are then removably secured together by some insulating material such as magnesium oxide, for example, and the outer end of the strip of ferromagnetic material is secured in an opening, provided in the housing. Since the effective, or working permeability of the core is determined in part by the spacing between the convolutions of the coil and by the amount of material comprising the core, the effective permeability of the core can be adjusted by varying the amount of material comprising the core and by changing the spacing between some, at least of the convolutions of the spiral core.

An object of the present invention is to provide a nominally fixed inductance having means for making a correcting adjustment.

A further object of the present invention is to provide Patented. 1., 19$

ar -improved toroidal inductance having a ferromagnetic core made from a spiral strip 'of ferromagnetic material, at least one end of said strip being adjustablyfixed 'so that the amount of material comprising the core canbe and so that the spacing between at least some of varied, the convolutions of the "spiralmay be adjusted, to vary the permeability of the core.

Other objects and many of the attendant advantages of this invention will be readily appreciated as they become better understood by references to the following detailed description when considered in connection with the accompanying drawings in which like reference mfmerals designate like partsthroughout the figures thereof and wherein:

Fig. l is a sectional view of taken on line 11 of'Fig. 2

gig 2 is a sectional view taken on line 2-7; of Fig. 1; an

Fig. 3 is an enlarged sectional view illustrating one means of securing the strip o'f'ferromagneticmaterial to the housing.

Referring now to the Figs. 1 and 2 wherein for the purpose of illustration there is shown a preferred enibodiment of this invention, the inductance comprises a hollow toroidal housing or casing 10, made of'a nonmagnetic and nonconducting material such as hard rubber, glass, Bakelite, or the like, having an inner wall 11, an outer wall 12, and side walls 13 "andf14'. In outer wall 12 there is provided an opening 15.

A core 16, made from a spirally wound strip of a ferromagnetic material such as Mumetal, a nickel-iron alloy, or the like, is located within housing 10. The convolutions of the core 16 are removably secured together by an insulating material, such as magnesium oxide. The outer end 17 of the spirally wound strip of ferromagnetic material comprising core 16 is loosened from the remainder of core 16 and is placed through opening 15 in housing 10. To complete the inductance, a coil 18 of insulated conductor 19 is wound around housing 10. However, opening 15 is not covered.

The amount of material comprising core 16 is chosen larger than necessary to make the inductance of coil 18 greater than that for which the coil is designed. The outer end 17 of the core 16 is then gradually pulled through opening 15. This of course reduces the amount of material comprising core 16 and changes the spacing between at least a portion of the two outermost convolutions of the core 16. In this way the effective permeability of the cores is reduced, decreasing the inductance of coil 18. If too much material is removed from core 16, a portion of the strip may be pushed back within the opening 15. In this manner the value of the inductance can be adjusted until it is equal to the desired value. When this condition is reached, the portion of the spiral strip extending through opening 15 is fixed as by glue 21 (Fig. 3) for example, to the housing 10, and the excess material is then removed.

As a result of this construction, it is possible to mass produce inductances which, after assembly, may be readily adjusted to any desired magnitude of inductance in the manner described above.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as herein specifically described.

What is claimed and desired to be protected by Letters Patent of the United States is:

1. In an inductance, a hollow toroidal casing having an inner wall, an outer wall having an opening therein and two side walls, said casing being formed from a substantially nonmagnetic material, a spirally coiled strip of ferromagnetic material inside said casing, the convolutions of said strip being removably secured together by an insulating material, one end of said strip being located in said opening in the outer wall of the casing, and means securing said end of said spirally coiled strip to said casing at said opening.

2. In an inductance, a hollow toroidal casing formed from a substantially nonmagnetic material, means forming an opening in said casing, a spirally coiled strip of one form of the invention ferromagnetic material inside said casing, the convolutions of said strip being removably secured together by an insulating material, one end of said spirally coiled strip being located in said means forming an opening in said casing, and means securing said one end of said spirally coiled strip to said casing at said means forming said opening.

3. An inductance comprising a hollow toroidal housing having at least an outer wall, said casing being formed from a substantially nonmagnetic material, means forming an opening in the outer wall of said housing, a spirally coiled strip of ferromagnetic material located within said housing, the convolutions of said strip being removably secured together by an insulating material, one end of said strip protruding through said means forming an opening in the outer wall of the housing, a coil of an insulated conductor wrapped around at least a portion of said housing, and means securing said one end of said strip to said housing.

4. An inductance comprising; a hollow toroidal casing having an opening therein, said casing being formed from a substantially nonmagnetic material, a spiral coil strip of ferromagnetic material located within said casing, the convolutions of said strip being removably secured to gether by an insulating material, one end of said strip protruding through the opening in the casing, a coil of an insulated conductor wrapped around at least a portion of said casing, and means securing said one end of said strip to said casing.

5. An inductance comprising; a hollow toroidal casing having an opening therein, said casing being formed from a substantially nonmagnetic material, a coiled strip of ferromagneti said casing, the strip b by an insulating materia through the opening in th and a coil of an insulated cond least a portion of said casing.

6. An inductance comprising; having an opening therein, a substantially nonmagne c material linearly removable located within eing removably secured together 1, one end of said strip protruding e casing to facilitate unwinding uctor wrapped around at a hollow toroidal casing said casing being formed from no material, a coiled strip of ferromagnetic material linearly removable located within said casing, the strip by an insulating materi of said strip to said casing at the opening.

References Cited in the file of this patent UNITED STATES PATENTS being removably secured together al, one end of said strip protruding through the opening in t a coil of an insulated conduc a portion of said casing, and means se he casing to facilitate unwinding, tor wrapped around at least curing said one end 

